The Impact of Comorbidity on Survival of Danish Colorectal Cancer Patients from 1995 to 2006-A Population-Based Cohort Study

PURPOSE: The impact of comorbidity on the outcome of colorectal cancer is poorly understood. We examined the prevalence of comorbidity and its impact on survival among Danish colorectal cancer patients. METHODS: The hospital discharge registries in northern Denmark were used to identify 13,190 patients diagnosed with colorectal cancer between 1995 and 2006, and to assess their comorbidity using the Charlson Comorbidity Index. We obtained product limit estimates of 1-year and 5-year crude survival based on three levels of comorbidity. To quantify the impact of comorbidity on mortality, we used Cox's proportional hazards regression analysis to compute the mortality rate ratio. RESULTS: One-third of the patients had recorded comorbid conditions. Patients with moderate and severe comorbidity (Charlson scores 1-2 and score 3+) had considerably higher 1-year and 5-year mortality rates compared to patients without comorbidity. For colon cancer patients, 1-year estimates in 2004 to 2006 were mortality rate ratio(1-2) = 1.2 (95 percent confidence interval, 1.0-1.5) and mortality rate ratio(3+) = 1.8 (95 percent confidence interval, 1.4-2.3). For rectal cancer patients with severe comorbidity, the negative impact on survival increased over time. CONCLUSIONS: Comorbidity was a strong negative prognostic factor for survival among colorectal cancer patients.